Various methods are currently used for synchronization, that is, for finding the position of the angle of the crankshaft of the internal combustion engine when starting. In a first method, the rundown position of the crankshaft is determined as the internal combustion engine is shut off, and this information is stored in the engine control unit until a restart. This method is also referred to as rundown detection and involves greater uncertainties since, for instance, the internal combustion engine could be turned over when the ignition is switched off and thus when the control unit is turned off, for example, by pushing the vehicle when the gear is engaged. This first method is also called synchronization stage 1.
In a second method, a signal of a camshaft sensor is evaluated, the associated camshaft sensor wheel being suitably designed to allow for the position to be found as quickly as possible. Such a sensor wheel is also known as a quick-start sensor wheel. In internal combustion engines that have an adjustable camshaft, this type of synchronization involves uncertainties because it is possible that at the time of the start the camshaft is erroneously not engaged. This method is also called synchronization stage 2. In a third method, the crankshaft sensor and the camshaft sensor are evaluated at the time of the gap in the crankshaft sensor wheel. This type of synchronization involves the least uncertainty since the crankshaft position and camshaft position associated with the gap in the sensor wheel can be determined reliably. Such a method is also known as synchronization stage 3.
The aforementioned methods of synchronization can run in parallel to each other. The higher the synchronization stage, the lower is the uncertainty in ascertaining the crankshaft angle. The synchronization stage respectively reached while the crankshaft of the internal combustion engine begins to rotate when starting the internal combustion engine may be indicated, for example, by a variable stored in a control unit.
As soon as the synchronization has occurred, angularly synchronous computation grids (also known as tasks) may be executed, which are able to trigger a fuel injection or a firing of a cylinder, for example. The position of the angularly synchronous computation grids relative to the top dead center of a reference cylinder is normally adjustable. At different crankshaft angles, different computation grids having different functions may be executed.
Thus, as soon as the crankshaft begins turning when starting an internal combustion engine, angularly synchronous computation grids may be started according to the information of a rundown detection or of the camshaft sensor in synchronization stage 1 or 2. Engine control functions such as an injection or ignition, for example, which are processed in these angularly synchronous computation grids, may indeed be called up when starting the internal combustion engine, but it may happen that an actual triggering of the corresponding output stage, for example of the ignition or the triggering of an injector or the like, must be suppressed until synchronization stage 3 is reached, that is, until the crankshaft angle may be determined with the greatest possible accuracy.
Reaching synchronization stage 3 thus means that the crankshaft sensor wheel gap or, in the case of a sensor wheel having an asynchronous graduation, the asynchronous arrangement of teeth and tooth gaps replacing the sensor wheel gap, must have been detected. The sensor wheel gap is defined by the installation of the sensor wheel and depends on the particular model of the internal combustion engine and may be located, for example, at 50° crankshaft angle before the top dead center (TDC) of a reference cylinder.
Various boundary conditions may require that a particular angularly synchronous computation grid be situated at a defined angle before the top dead center. In addition it may be the case that the accuracy of an engine control function computed in this computing grid requires that, when starting the internal combustion engine, computations or computation outputs may occur only at synchronization stage 3, that is, that a particular functionality must always wait for a detected gap in the sensor wheel before being executed when starting the internal combustion engine.
In this context it may happen that the start of the internal combustion engine coincides with a crankshaft angle at which the angularly synchronous computation grid for a function was just exceeded. Thus, for example, if the start of the internal combustion engine begins at a crankshaft angle of 50° before the top dead center of a cylinder, and if an angularly synchronous computation grid for a specific functions begins, for example, 60° before the top dead center of the cylinder, then this function is executed only after the crankshaft angle of 50° before the top dead center of the cylinder has been reached again. This means that the associated function is executed only at a considerably later time, that is, after one crankshaft rotation.